FIG. 11 is a circuit diagram explaining an electrical circuit for an automotive vehicle mounted with a conventional automotive alternator such as that described in Japanese Patent Laid-Open No. SHO 57-101549 (Gazette), for example, and FIG. 12 is a cross section showing a construction of a power supply mechanism portion in the conventional automotive alternator.
In conventional automotive alternators, when a key switch 105 is closed, an electric current flows from a storage battery 104 through the key switch 105, a positive electrode brush 109, a field winding (a rotor winding) 102, and a negative electrode brush 110 to a power generation control apparatus 108. The field winding 102 is excited with a direct current by this electric current.
In this state, when a rotor is driven to rotate by rotation of an engine, a rotating magnetic field is applied to an armature winding (a stator winding) 101, giving rise to an electromotive force in the armature winding 101. This alternating-current electromotive force is converted into a direct current by a three-phase full-wave rectifier 103, and serves to charge the storage battery 104. This alternating-current electromotive force is also converted into a direct current by an auxiliary rectifier 107 and is supplied to the field winding 102. As the rotational speed of the rotor rises, the power generation control apparatus 108 controls the electric current flowing through the field winding 102 such that the voltage of the storage battery 104 is constant.
Now, the positive electrode brush 109, as shown in FIG. 12, is housed inside a brush holder 125 so as to be pushed outside by a force from a coil spring 126. Moreover, although not shown, the negative electrode brush 110 is also similarly housed inside the brush holder 125. Thus, the positive electrode brush 109 and the negative electrode brush 110, due to the force from the coil springs 126, slide in contact with slip rings (not shown) functioning as current receiving portions rotating together with the rotation of the rotor, tip portions thereof being gradually abraded. The electric current flows through the positive electrode brush 109, a slip ring, the field winding 102, and a slip ring to the negative electrode brush 110.
A light source 113 and a photodetector 114 are disposed on the brush holder 125 so as to face each other on mutually opposite sides of the positive electrode brush 109. The light source 113 and the photodetector 114 are constituted by a light-emitting diode and a phototransistor, for example, and are disposed facing the brush holder 125 so as to correspond to an allowable push-out limit position of the positive electrode brush 109.
Thus, in a normal state, the positive electrode brush 109 is between the light source 113 and the photodetector 114, and the photodetector 114 does not receive any light from the light source 113. Then, when the positive electrode brush 109 is abraded to the abrasion limit, the photodetector 114 receives light from the light source 113, and an electric current flows. This electric current is amplified by a transistor 115, and is converted by a Zener diode 118 so as to obtain a constant voltage. This constant voltage is applied to an astable multivibrator 112, and the astable multivibrator 112 performs low-frequency oscillation. Because an electric current from a neutral point 111 placing a transistor 116 in an ON state by means of a diode 119 and a resistor 124 flows into the astable multivibrator 112 through a resistor 123 while the output state of the astable multivibrator 112 is at a low level, the transistor 116 is placed in an ON or an OFF state depending on whether the output state of the astable multivibrator 112 is low level or high level. A transistor 117 is switched OFF when the transistor 116 is ON, and the transistor 117 is switched ON when the transistor 116 is OFF. In addition, while the transistor 117 is placed in the ON state, an indicating lamp 106 is lit.
In other words, when the positive electrode brush 109 is abraded to the abrasion limit, the astable multivibrator 112 performs low-frequency oscillation, and the indicating lamp 106 is placed in a periodic flashing state (an abrasion limit sensing indicating state). Thus, by checking for the periodic flashing of the indicating lamp 106, a vehicle occupant can recognize that the positive electrode brush 109 has abraded to the abrasion limit and can perform brush replacement. Moreover, if the light source 113 and the photodetector 114 are disposed on the brush holder 125 so as to face each other on mutually opposite sides of the negative electrode brush 110, the abrasion limit of the negative electrode brush 110 will be detected. Moreover, power generation is stopped if either the positive electrode brush 109 or the negative electrode brush 110 reaches the abrasion limit, and current supply to the field winding 102 is no longer performed.
However, in conventional automotive alternators, the slip rings rotate during vehicle operation, and the positive electrode and the negative electrode brushes 109 and 110 are constantly and continually being subjected to vibration and fluctuation. When roundness of the slip rings deteriorates, the vibration and the fluctuation of the positive electrode and the negative electrode brushes 109 and 110 increase further. There are also influences such as noise, etc., causing detection output from the photodetector 114 to fluctuate. For these reasons, one disadvantage has been that malfunctions may arise such as the abrasion limit sensing indicating state being entered before the brushes 109 and 110 reach the abrasion limit, or the abrasion limit sensing indicating state not being entered even if the brushes 109 and 110 reach the abrasion limit, etc., reducing the reliability of brush abrasion limit sensing.
Furthermore, in conventional automotive alternators, a constant voltage from a Zener diode 118 is used as an activating power source for the astable multivibrator 112. However, there are cases in which the electric current flowing through the photodetector 114 deteriorates significantly due to the effects of the vibration of the brushes, etc. In other words, the reliability of the supply of current from the photodetector 114 to the astable multivibrator 112 is low. Because the amplitude of pulse waveforms of this astable multivibrator 112 is dependent on the activating power source, if the electric current flowing through the photodetector 114 drops, the amplitude of those pulse waveforms decreases, hindering the operation of the transistors 116 and 117 and the lighting of the indicating lamp 106. Thus, another disadvantage has been that even if the brush abrasion limit is sensed normally, there may be insufficient electric power to activate the indicating lamp 106, making it difficult to confirm the periodic flashing of the indicating lamp 106.
In addition, in conventional automotive alternators, because the brush abrasion limit detection and display circuits are constructed independently from the power generation control apparatus 108, another disadvantage has been that the number of parts and costs are increased.